A stator structure with radial winding is constituted by stacking a plurality of pole pieces of the same shape and winding metal conductor around the pole teeth, wherein the pole piece structure is as shown in FIG. 1. The pole piece formed by punching a plate material with a proper thickness and an excellent magnetic property includes a hub 10 having a hole 11 at the center, a plurality of poles 12 (six in FIG. 1) integrally formed with the hub 10, extended from the periphery of the hub 10 to radiate in a radial direction, and having a pole shoe 13 expanded from an end of each pole in a tangential direction, in which those poles 12 extended in a radial direction are wound around by metal conductor to form a stator structure with radial winding, and the pole shoe 13 that is tangentially expanded serve as the end of a sensing pole of the stator structure with radial winding.
The bigger the end (i.e. pole shoe) of the sensing pole of the stator structure with radial winding is, the larger the overlap region of interphase inductance and torque of a motor is. This effect will result in stronger self-starting capability, large output torque, and little torque ripple of a motor. In contrast, the larger the pole shoe 13 of the pole piece is, the smaller the gap between two adjacent pole shoes 13 will be, rendering the job of winding metal conductor even tougher.
If a mechanical angle β of the width of the pole shoe 13 is divided by a mechanical pole pitch angle θ of two adjacent poles 12, a ratio α is obtained.
      β    θ    =  αThe value of α is proportional to the angle of β, that is, the more the angle of β is, the larger the value of α is. The values of α for the existing pole piece structures of stator with radial winding are all within a range of 0.65˜0.85.
What the electronic information products and consumer electronics are concerned about nowadays is a high-efficiency operation. Hence, the demand for motor performance is getting higher. Whereas, the form of pole piece defined by such ratio (0.65˜0.85) is unable to make the most of the performance of motor, making the pole piece fail to keep abreast with the increasingly strict demand for motor performance from the industries.